Archaeologists call it the Persian carpet effect.

Imagine you're a mouse running across an elaborately decorated rug. The ground would merely be a blur of shapes and colors. You could spend your life going back and forth, studying an inch at a time, and never see the patterns.

Like a mouse on a carpet, an archaeologist painstakingly excavating a site might easily miss the whole for the parts. That's where the work of aerial photographers such as Georg Gerster comes in.

For four decades, Gerster, 77, has been flying over sites from the Parthenon to Ayers Rock to provide archaeologists with the big picture. Seen from high above, even the most familiar turf can appear transformed, with a coherence and detail invisible on the ground.

"In the Middle Eastern and classical [archaeology] world, it's a tool people recognize as extremely valuable," says archaeologist William Sumner, a University of Chicago professor emeritus, of aerial photography. "The thing about Georg's images is they are superb. If there's anything to be seen, it's in his images."

In Gerster's recent book, The Past From Above: Aerial Photographs of Archaeological Sites (J. Paul Getty Museum), places we've seen a thousand times in pictures from ground level take on a whole new meaning. His photographs dramatize the scale of ancient structures and show them, as if for the first time, in relation to their surroundings.

Stonehenge, so impressive at eye level, is a little underwhelming from above; the Great Wall of China appears shockingly large. And some mysterious structures -- the Nazca lines, 300 giant figures etched into desert sand beginning in 200 B.C. and located south of Lima, Peru, for example -- seem as if they were designed to be seen from above.

Gerster, who was born in Switzerland and lives near Zurich, developed a passion for aerial photography in 1963, when, at 35, he chartered a small plane to photograph Egyptian and Sudanese sites about to be flooded by construction of the Aswan High Dam. Since then, he has photographed sites in 108 countries and Antarctica, usually while perched in an open doorway as his plane or helicopter roars over a site.

Not a new idea

Of course, the urge to get above it all has obsessed photographers since the invention of the camera. The first known aerial photograph was taken from a balloon in 1858.

But not until the invention of the airplane did the idea of photographing ruins become practical. Even then, it was usually a byproduct of military reconnaissance. German pilots documented Egypt's pyramids during World War I. Between the wars, British military fliers made important advances in aerial photography.

Even aviator Charles Lindbergh found the idea captivating, making low flights over the jungles of Central America in 1929 to search for hidden Mayan ruins while his wife, Anne, took photographs.

Modern technology has only expanded archaeologists' interest in aerial imaging. Today, "landscape archaeology" is one of the field's hottest disciplines, combining satellite imagery (including declassified spy photos from the 1960s) with Global Positioning System data to tease out a landscape's hidden details, such as long-buried roads and canal systems.

Not welcome everywhere

Yet, despite growing academic acceptance (and even appetite) for aerial archaeology, there are places where it has become a virtual impossibility. In unstable areas of the Middle East -- a region rich in photogenic ruins -- aerial photographers are viewed with hostility. "All the secrecy is ridiculous, but still when you come and want to take aerial photographs, you're regarded as a spy," says Gerster.

That pressure makes Gerster's work from the 1960s and '70s all the more valuable. "A lot of the areas he covered are denied to us today because of the suspicion of archaeologists," says Harvard University landscape archaeologist Jason Ur. "I just can't get good low-level aerial photography of Syria."

Since Gerster visited Iraq in 1973, many of the sites he documented have been damaged by war and looting. As politics, development and time take their toll on the world's precious ruins, the irreplaceable images by Gerster and others become even more important portraits of the past.